One type of hybrid electric vehicle (HEV), commonly referred to as a mild hybrid vehicle or mild HEV, includes an engine and a belt-driven starter generator (BSG) unit. The BSG unit includes a battery system (e.g., 48 or 400 volts) that supplies a current to drive an electric motor, which in turn drives a crankshaft of the engine via a belt to assist in starting or restarting the engine. This enables the engine, for example, to be periodically turned off during certain operating periods and then quickly restarted when drive torque is required. This is also commonly referred to as engine start/stop engine operation. Such operation provides for increased fuel economy. The BSG unit is also configured to convert torque generated by the engine at the crankshaft to electrical energy for powering or recharging components, such as the battery system of the BSG unit.
A DC-DC converter is optionally implemented to step-down the voltage of the battery system to a lesser voltage (e.g., 12 volts) for recharging another battery (e.g., a lead-acid battery) that powers vehicle accessory loads and/or for directly powering the vehicle accessory loads. When a main contactor of the battery system opens due to a fault condition, a motor generator unit (MGU) typically maintains the voltage on the high voltage bus. The MGU's responsiveness, however, is relatively slow and it has a relatively low capacitance. Thus, additional energy storage devices (e.g., capacitors) must be implemented to adequately maintain the high voltage bus voltage, which increases costs, weight, and packaging space. This may additionally or alternatively require the use of a more expensive MGU capable of maximized responsiveness. Accordingly, while such electrified vehicle control systems work well for their intended purpose, there remains a need for improvement in the relevant art.